1. Field of the Invention
The present invention relates to a control system for an engagement pin employed in a drum-type weft storge unit which is mainly employed in a jet-loom for storing the weft and for measuring the same in length.
2. Description of the Prior Art:
It is widely known that the weft is wound on a drum in its outer periphery and stored therein, while subjected to a disengagement/engagement operation from/with the drum by the use of an engagement pin which moves forward and backward relative to the outer periphery of the drum.
In this unit, in order to deliver a predetermined length of the weft from the drum precisely, it is necessary to precisely control a time interval between a disengagement-time at which the engagement pin is retracted from the drum to disengage the weft from the drum and an engagement-time at which the engagement pin is projectecd or moved forward to the drum to engage the weft with the drum, and is also necessary to synchronously control both the disengagement and engagement times with a mechenical ratation-angle of the loom.
In a method for precisely control the engagement pin as described above, the disengagement-time is constantly established by the use of the mechanical rotation-angle of the loom; the number of winding times of the weft delivered from the peripheral surface of the drum is measured by means of a photoelectric sensor which is a so-called disengagement sensor; and the engagement-time is determined upon delivery of a predetermined length of the weft. However, in such method, since a speed of the weft traveling across an optical axis of the disengagement sesnsor is too large, there is an inevitable disadvantage in that the engagement pin is operated in an unstable manner.
In order to eliminate the above disadvantage, for example, Japanese Patent Laid-Open No. 60-65150 teaches a method in which: in place of the disengagement sensor, a so-called "weft feeler" is employed for checking whether the weft is normally picked or not, which weft feeler makes it possible to control the engagement-time of the engaement pin.
This prior art is excellent in that the disentgagement sensor may be omitted. In this prior art, a disenganement time Ts at which the weft is disengaged from the drum by the engagement pin is predetermined, and an arrival time Te at which the tip end of the weft arrives at that side of the woven cloth which is opposite the weft-insertion side is actually measured so that an engagement time Tc of the engagemenet pin is calculated by the following formula: EQU Tc =Te-(Te -Ts)/(2n)
where T is a mean amount of movement of the arrival time Te (i.e., a mean value of the arrival time Te in a predetermined number of successive weft-insertion cycles), and n is the number of turns of the weft disengaged from the drum for each picking.
The above formula is based on the fact that the engagement time Tc is between the arrival time Te at which the tip of n turns of the weft disengaged from the drum arrives at that side of the woven cloth which is opposite the weft-insertion side, and the disengagement time Tel at which (n-1) turns of the weft begins to be disengaged from the drum (i.e., Tel=Ts+(n-1)(Te-Ts)/n).
In this connection, it is to be noted that in order for the above formula for Tel to be correct, it must be presupposed that the travelling; speed of the weft during the period from the disengagement time Ts to the arrival time Te be held constant. That is the weft which is picked by a picking nozzle and shuttled must be inserted at a constant speed over the entire cycle of every picking motion, and such travelling speed of the weft must be precisely reproduced upon every weft insertion in order to optimize the engagment time Tc in the following weft-insertion cycle.
In general, the above presupposition is hardly met and hence it is not ensured that the above-described prior art can always give an optimal engagement time Tc. Consequently, if the above measure is reduced into practice, it is difficult to completely prevent variations in the length of the weft being delivered.